Cope with non-migrations django-subdomain-instances.

If we're not using migrations for django-subdomain-instances, then
Instance already has title and description fields by now, and as
they're not null they need to be filled in when creating instance
'default'.

Add title and description to 'instance' in the orm, and then set
them when creating a default instance if we're not using migrations
for django-subdomain instances. If we are using migrations, don't
add them to the orm at this point.
Don't try to change content types.

This migration was trying to change the (speeches, popolospeaker)
contenttype to be (speeches, speaker) which since 80e3f0b4325395951cf89,
probably already exists, causing an error.

Instead, just leave the old content types be - hopefully they're
only being used by admin records, etc.